Initially, most domestic timber framed construction was carried out on site by carpenters using a high level of skill in cutting, fitting, and building structures from basic packs of timber. Such construction required considerable time, knowledge of materials, and attention to detail through the entire build process to ensure a serviceable result. Weather also played an important part in the build time as the whole process occurred on site. The structures were generally of basic post and beam construction using checked-in timber diagonals to provide lateral stability.
A significant early innovation in the field was the introduction of timber roof trusses. These were prefabricated offsite to factory tolerances and, because of their “truss action,” could span much larger distances than conventional structures, with far less deflection and less timber. The roof structure was installed in a fraction of the time, was dimensionally accurate, and required far less skill to install. Offsite wall frame prefabrication followed, for the same reasons, to provide an engineered product, use of reduced materials and waste, and reduction of time and skilled labor on site. Again for the same reasons, floors followed suit, with the introduction of floor trusses and timber I-joists. More recently, light-gauge steel equivalent has been introduced to confer the same benefits as achieved by prefabrication of timber framing components.
Commonplace now is the delivery of packs of frames and trusses to site, with a team of three to five installers completing the erection of the structure of an average two-story house in two to three days. Most of the components are manually lifted into place, though relatively large and heavy parts may be lifted into place by crane.
There are a number of current trends, including trends towards smaller lot sizes, larger houses with more open spaces and a greater focus placed on site safety, which have given rise to comparatively more larger and heavier components and an increasing use of cranes, scaffolding and systems to protect installers working at heights, with attendant increases in site costs.
Offsite assembly of components into paneled units addresses these issues and significantly reduces installation time.
Provision for safe, cost-effective lifting of such units is highly desirable.